Sound insulation materials are used in a variety of settings where it is desired to dampen noise from an external source. For example, sound insulation materials have been used in applications such as in appliances to reduce the sound emitted into the surrounding areas of a home, in automobiles to reduce mechanical sounds of the motor and road noise, and in office buildings to attenuate sound generated from the workplace, such as from telephone conversations or from the operation of office equipment. Conventional acoustical insulation materials include materials such as foams, compressed fibers, fiberglass batts, felts, and nonwoven webs of fibers such as meltblown fibers. Acoustical insulation typically relies upon both sound absorption (the ability to absorb incident sound waves) and transmission loss (the ability to reflect incident sound waves) to provide adequate sound attenuation.
In automobiles, the insulation material also relies upon thermal shielding properties to reduce or prevent the transmission of heat from various heat sources in the automobile (such as from the engine, transmission, exhaust, etc.) to the passenger compartment of the vehicle. Such insulation is commonly employed in the automobile as a headliner, dash liner, or firewall liner. Liners are typically formed of laminates of (1) one or more layers of an insulation material to provide desired mechanical strength properties and (2) one or more additional layers of a rigid material to permit simple and convenient installation in the automobile as well as proper functional performance.
Laminate materials may be conventionally formed by depositing a layer of loose chopped glass fibers onto an adhesive layer positioned on a scrim on a moving conveyor. A second adhesive layer is then placed onto the glass fibers to keep the glass fibers in place. If the laminate is to be used to form a headliner for an automobile, polyurethane boards are placed onto the second adhesive, and sequential layers of adhesive, chopped glass fibers, and adhesive are placed onto the polyurethane boards. The layered material is then passed through a lamination oven where heat and pressure is applied to form a composite material that can later be formed into a headliner.
One problem faced by manufacturers of these laminate composite materials is evenly distributing the chopped glass fibers onto the adhesive layer(s). If a uniform distribution of glass fibers is not provided, the final composite material may have undesirable properties. Another problem with conventional processes that use loose chopped glass is that adding the chopped glass during the manufacturing process is slow and costly. In addition, loose glass has the potential to be skin irritating if the fibers come into contact with the workers forming the laminated material.
One solution to the problems associated with the use of loose chopped glass has been to substitute a glass mat for the loose chopped glass. In one conventional process, glass roving is chopped on a conveyor system and a thin adhesive spunbond material is placed on top of the glass. A second layer of chopped glass is positioned on the spunbond material, forming a sandwich-like material of chopped glass/spunbond adhesive/chopped glass. The three-layered material is passed through a laminating oven to form a chopped glass mat. The mat may then be used in the production of a headliner as a substitute for the loose chopped glass used in other conventional processes. However, conventional mats using chopped roving are costly to manufacture. In addition, the mats do not have a porous structure to aid in the acoustical performance of the final product.
Therefore, there exists a need in the art for a non-woven mat for use as a reinforcement material in liners in automotive applications that exhibits superior sound attenuating properties, has improved structural, acoustical, and thermal properties, and that is lightweight and low in cost.